The present invention relates to a photosensitive composition, a photosensitive planographic printing plate precursor, and a method for manufacturing the planographic printing plate precursor.
A planographic printing plate used in the field of offset printing has hitherto been produced by bringing a silver salt mask film having an image previously formed thereon into close contact with a photosensitive planographic printing plate comprising a substrate and a photosensitive layer provided on the substrate, and subsequently exposing the entire surface to activating light rays, thereby to transfer the image onto the photosensitive planographic printing plate, followed by wet development, post-treatment, and drying processes.
Examples of light sources of activating light rays used in these processes include mercury lamps, metal halide lamps, xenon lamps, chemical lamps, carbon arc lamps, and the like. The photosensitive layer of the photosensitive planographic printing plate is designed to be sensitive to light having a wavelength in a range of from 300 to 450 nm corresponding to an output wavelength of these light sources.
Such photosensitive planographic printing plates include, for example, positive-working photosensitive planographic printing plates, which can be developed with a developer of an aqueous alkali solution (hereinafter referred to as an alkali developer). As positive-working photosensitive compositions used in a photosensitive layer of such a positive-working photosensitive planographic printing plates, photosensitive compositions containing an alkali-soluble resin, such as a novolac resin, and a quinone diazide compound, are known.
In addition, a negative-working photosensitive planographic printing plate, which can be developed with an aqueous alkali developer, is also known. Examples of the negative-working photosensitive compositions used in the photosensitive layer of the negative-working photosensitive planographic printing plates include photosensitive compositions containing an alkali-soluble resin and a photosensitive diazonium compound, and photosensitive compositions containing an alkali-soluble resin, an ethylenically unsaturated compound, and a radical polymerization initiator.
With the progress of computer image processing techniques, a method of directly writing an image by irradiation with light corresponding to a digital signal has recently been developed. Intense interest has been shown towards a computer-to-plate (CTP) system of directly forming an image on a photosensitive planographic printing plate without outputting to a silver salt mask film, by utilizing this system in a planographic printing plate. As a light source for irradiation with light, a laser having a maximum intensity in the ultraviolet, visible or infrared range of from 300 nm to 1200 nm, such as an Ar ion laser, a YAG laser, a Hexe2x80x94Ne laser, or a semiconductor laser, can be used. The CTP system using a high-output laser having a maximum intensity within a near infrared or infrared range has such advantages that a high-resolution image can be obtained by exposure in a short time and a photosensitive planographic printing plate used in the system can be handled in a lighted room. In particular, high-output, small lasers are easily available as a solid laser and a semiconductor laser, which emit infrared rays having a wavelength in a range of from 760 nm to 1200 nm.
As the positive-working photosensitive composition that can form an image using the solid laser or semiconductor laser capable of emitting infrared light, a photosensitive composition comprising an alkali-soluble resin (such as a novolac resin) and a photothermal conversion material (for example, an infrared absorber such as a dye or pigment) is known.
As the negative-working photosensitive composition that can form an image using the solid laser or semiconductor laser capable of emitting infrared light, a photosensitive composition comprising an alkali-soluble resin (such as a novolac resin), an acid crosslinking agent (such as a resol resin), a compound capable of generating an acid by means of heat (for example, an acid generating agent), and a photothermal conversion material (for example, an infrared absorber such as a dye or pigment) is proposed in Japanese Unexamined Patent Application, First Publication No. Hei 7-20629.
As the negative-working photosensitive composition that can form an image using a laser that emits infrared light from visible light, such as an Ar ion laser, a YAG laser, a Hexe2x80x94Ne laser, or a semiconductor laser, those comprising an ethylenically unsaturated compound, a sensitizing pigment having an absorption maximum in a range of from 400 to 1200 nm, and a photopolymerization initiator are proposed in Japanese Unexamined Patent Application, First Publication No. 2000-181059, and Japanese Unexamined Patent Application, First Publication No. Hei 2-244050.
Examples of the alkali-soluble resin used in the photosensitive layer of the alkali-developable photosensitive planographic printing plates include, for example, vinyl polymers having an acid group such as a carboxyl group, a phenolic hydroxyl group, a sulfonic acid group, a phosphoric acid group, a sulfonamide group, or an active imide group; a polyaddition polymer such as polyurethane; and polycondensation polymers such as polyesters, in addition to novolac resins. However, the photosensitive layer having an alkali-soluble resin had problems such as poor solvent resistance to the solvent contained in various printing chemicals (for example, washing oil, fountain solution, gum solution, plate preserver, and plate cleaner). In particular, it had a problem such that the resistance to a UV ink-washing oil used in UV ink printing was insufficient and the image portion became corroded with an organic solvent. As a result, it also had a problem such that the photosensitive layer was insufficient in terms of press-life, i.e., durability.
As the photosensitive composition having improved solvent resistance and improved durability, photosensitive compositions comprising a resin having a cyano group and a urea bond in the side chain are proposed in Japanese Unexamined Patent Application, First Publication No. Hei 8-339080. In addition, in Japanese Unexamined Patent Application, First Publication No. Hei 8-339082 and Japanese Unexamined Patent Application, First Publication No. 2000-330265, it is described that a photosensitive composition comprising a resin having a urea bond in the side chain has good solvent resistance and has good durability.
However, the photosensitive layer formed by the photosensitive composition described above is still insufficient in terms of solvent resistance and durability. In particular, a further improvement in resistance to the UV ink-washing oil used in UV ink printing had been required.
In addition, as a photosensitive composition having improved wear resistance, Japanese Unexamined Patent Application, First Publication No. Sho 63-261350 proposes a photosensitive composition comprising an alkali-soluble polyurethane resin having a sulfonylureide group and the like in the side chain, and Japanese Unexamined Patent Application, First Publication No. Sho 63-287943 proposes a photosensitive composition comprising an alkali-soluble poly(urethane-urea) resin having a carboxyl group.
Furthermore, as a photosensitive planographic printing plate having improved durability, a photosensitive planographic printing plate having a photosensitive layer formed from a cyano-group-containing resin is proposed in Japanese Unexamined Patent Application, First Publication No. 2000-199950.
However, in any one of the photosensitive compositions described above, solvent resistance and wear resistance were insufficient, and the photosensitive planographic printing plates produced using these photosensitive compositions also were not sufficiently satisfied.
In addition, a method for improving durability by subjecting a planographic printing plate obtained after a developing treatment to a heat treatment (hereinafter, referred to as a baking treatment) to cure an image part is described in, for example, GB Patent No. 1,151,199 and GB Patent No. 1,154,749. The baking treatment is generally carried out by heating a planographic printing plate for 1 to 60 minutes at 180 to 320xc2x0 C.
However, in some photosensitive compositions forming a photosensitive layer, the problems such as occurrences of quality deterioration due to baking, or lack of the image parts (microlines) might occur.
See also: (1) Japanese Unexamined Patent Application, First Publication No. Hei 7-20629; (2) Japanese Unexamined Patent Application, First Publication No. 2000-181059; (3) Japanese Unexamined Patent Application, First Publication No. Hei 2-244050; (4) Japanese Unexamined Patent Application, First Publication No. Hei 8-339080; (5) Japanese Unexamined Patent Application, First Publication No. Hei 8-339082; (6) Japanese Unexamined Patent Application, First Publication No. 2000-330265; (7) Japanese Unexamined Patent Application, First Publication No. Sho 63-261350; (8) Japanese Unexamined Patent Application, First Publication No. Sho 63-287943; (9) Japanese Unexamined Patent Application, First Publication No. 2000-199950; (10) GB Patent No. 1,151,199; and (11) GB Patent No. 1,154,749.
Thus, an object of the present invention is to provide a photosensitive composition that can provide a coating film having superior solvent resistance and superior wear resistance, and to provide a photosensitive planographic printing plate that can be subjected to a baking treatment, having superior solvent resistance particularly resistance to a UV ink-washing oil used in UV ink printing, having superior durability, and exhibiting superior exposure visible image properties.
After intensive research in order to achieve the object described above, the present inventors discovered that a phenol resin having a urea bond in the main chain exhibits the effect of improving the solvent resistance and wear resistance of the coating film, thus completing the present invention.
That is, a photosensitive composition of the present invention is characterized by comprising a phenol resin having a urea bond in the main chain.
Furthermore, the phenol resin preferably a resin produced by condensation polymerization between dimethylolurea and any one monomer selected from the group consisting of phenols, bisphenols, hydroxynaphthalenes, and condensates of p-cresol/formaldehyde having a low molecular weight.
Furthermore, in the phenol resin, the phenolic hydroxyl group is preferably functionalized with an ether group, an ester group, a urethane group, or a carbonate group.
Furthermore, the phenol resin preferably has a structural unit represented by general formula (A): 
wherein I=1, 2, 3, or 4; m=0, 1, 2, or 3; n=0, 1, 2, or 3; I+m+n=1, 2, 3, or 4; k represents a repeating unit number; R represents an ether residue, an ester residue, a urethane residue, or a carbonate residue; and Rxe2x80x2 represents a monovalent organic group having not more than 20 carbon atoms, which may be substituted.
In another aspect, the photosensitive composition preferably comprises an o-quinone diazide compound.
In another aspect, the photosensitive composition preferably comprises a photosensitive diazonium compound.
In another aspect, the photosensitive composition preferably comprises an ethylenically unsaturated compound and a radical polymerization initiator.
In another aspect, the photosensitive composition preferably comprises a photothermal conversion material.
In another aspect, the photosensitive composition preferably comprises an acid generating agent, an acid crosslinking agent, and a photothermal conversion material.
A photosensitive planographic printing plate precursor according to the present invention is characterized by comprising a substrate and a photosensitive layer formed from the photosensitive composition according to the present invention provided on the surface of the substrate.
A method for manufacturing a planographic printing plate according to the present invention is characterized by comprising the steps of: exposing a photosensitive layer of the photosensitive planographic printing plate precursor according to the present invention to activating light rays, in a state of bringing a mask film of a silver salt having an image previously formed thereon into close contact with the photosensitive layer; and developing the photosensitive planographic printing plate obtained after the exposing step with an aqueous alkali solution.
In addition, a method for manufacturing a planographic printing plate according to the present invention is characterized by comprising the steps of: forming a latent image on a photosensitive layer of the photosensitive planographic printing plate precursor according to the present invention, using a laser beam based on digital image information; and developing the imaged photosensitive planographic printing plate precursor obtained after the step of forming the latent image with aqueous alkali solution.
Furthermore, the method for manufacturing a planographic printing plate according to the present invention may comprise the step of baking treating by subjecting the photosensitive planographic printing plate obtained after the developing step to a heat treatment.